What is the greatest common factor of $20$ and $25$ ? Another way to say this is: $\operatorname{gcf}(20, 25) = {?}$
Solution: The greatest common factor is the largest number that is a factor of both $20$ and $25$ The factors of $20$ are $1$ $2$ $4$ $5$ $10$ , and $20$ The factors of $25$ are $1$ $5$ , and $25$ Thus, the greatest common factor of $20$ and $25$ is $5$. $\operatorname{gcf}(20, 25) = 5$